This invention relates generally to energy efficient washing machines for cleansing clothes and similar articles and more particularly to washing machines that consume only the optimal amount of water that is required for the size of the load of articles to be cleaned.
On most conventional washing machines, the amount of water that the machine uses in a washing cycle is determined by the operator via a manual control, such as a load size selector switch. Such manual controls typically offer a limited number of selections (e.g., small, medium, or large); such selections may not offer a load size option appropriate for a given load. It is also common that a larger size load is selected than is actually needed to achieve effective cleaning of the articles to be washed. Use of more water than is needed for effective cleaning leads to a waste of water and of energy used to heat and circulate the water.
Automated control of water added to the washer during a wash cycle has been suggested as one means of minimizing energy usage in a washer. Typically the most important factor in determining the appropriate amount of water to provide effective cleaning is the weight of the articles to be cleaned. In washers having advanced motor controls so that a given torque can be commanded (such as a Switched Reluctance Motor (SRM), electronically commutated mortor (ECM), or the like), the determination of clothes weight can be done by measuring the torque and then determining the inertia of articles in the washer basket. Determination of this inertia cannot, however, be readily accomplished if one cannot directly control or measure torque of the motor driving the basket, such as is the case with conventional electrical induction motors without special controls. Command torque motors such as the SRM are more complex and expensive than the commonly-used induction motors; similarly, inferred or direct measurement of torque typically requires use of equipment that results is more complex and expensive than is desirable in household appliances due to the need for complex power electronics in the appliance, or the use of extra sensors for determining the torque.
It is desirable to provide the energy-saving advantages of load determination without the necessity of having equipment in the washing machine that makes it more complex and expensive. It is thus an object of one embodiment of this invention to provide an energy efficient method of operating a washing machine using a normalized inertia-based load determination in a machine in which torque is not readily directly commanded or set. Such an inertia-based system is readily adapted for use in a washing machine in which the drive motor for the basket is either a single speed or a multiple speed electric induction motor.